The present invention relates to a balloon catheter that is particularly suitable for medical tests carried out using a cardiac catheter.
In the cardiac field, recently, catheter therapeutic treatment and a surgical treatment have been carried out. For the therapeutic treatment of the heart, cardiac function and blood flow dynamics must be assessed exactly. In addition to the assessment at a constant state thereof, the assessment of cardiovascular function corresponding to a change under load enables a preliminary assessment of cardiac function and potential lesions. Based on the relationship between ventricular pressure and volume under a decrease of a preload due to a temporary occlusion of the inferior vena cava, for example, there can be deduced a cardiac contraction, a cardiovascular linkage relation and a ventricular energy relation that are not influenced by the load. For such assessment, a balloon catheter is temporarily used to occlude a blood vessel.
As shown in FIG. 4, generally, a small inflatable balloon 10 is mounted on the head of a balloon catheter. By inflating the balloon 10, a blood vessel can be occluded. Generally, the small inflatable balloon 10 is in the shape of a tube (not shown) or a ball (as shown in FIG. 4) when deflated. Since the ball-like balloon is usually made of latex or a rubber-like material such as silicone rubber or polyisoprene, the ball-shape balloon has higher extension and shrinkage. Therefore, the balloon 10 preferably has a ball shape when the diameter of the inflated balloon is required to be 5-fold or more the diameter of the balloon before inflation in order to occlude the blood vessel.
However, the balloon in the shape of a ball has a diameter larger than the balloon in the shape of a tube when deflated. Thus, the deflated balloon in the shape of a ball usually has a diameter of about 2 mm to 5 mm and a thickness of 0.1 mm to 0.5 mm, and is liable to be caught on a check valve or a head of an introducer sheath that inserts the balloon into the body of a patient, so that there is a potential risk of damage to the balloon. When an introducer sheath of a larger size is used so as to avoid such a problem, the risk of damage to the blood vessels, especially the cardiovascular system of a patient is disadvantageously increased.
In U.S. Pat. No. 5,853,389, there is disclosed a balloon for a balloon catheter which comprises a tubular central section and transition sections folded in pleats as urged by spiral ridges on either end of the central section connecting with tubular end sections of less diameter than the central section. But the balloon catheter of this reference is relatively long compared with the diameter thereof, and the introduction into an introducer sheath is troublesome. Further, the deflated diameter of the central section may be more than one fifth of the diameter in a fully inflated condition because the material of the balloon may not be an expandable material such as latex and rubber-like materials and the central section has a plural of pleats as shown in FIG. 6 of this reference.
Under such circumstances as described above, the present invention has been achieved. It is a purpose of the present invention to provide a balloon catheter which can readily occlude blood vessels, of which the balloon is of a small diameter when deflated, and for which a thinner introducer sheath can be used.
The inventors have made investigations so as to overcome the problems and have thought that by mounting a ball-shaped balloon in the form of a screw on the shaft, the diameter of the balloon when deflated can be put at an optimum dimension. Thus, the present invention has been achieved. More specifically, the present invention relates to a balloon catheter comprising a deflated balloon in the shape of a ball as mounted in the form, or shape, of a screw on a distal end of a shaft. Herein, the balloon in the form of a screw can be mounted by fixing one end of a hollow ball, both ends of which are open on the shaft, modifying the shape of the ball in the form of a screw by twisting the ball and fixing the other end on the shaft.